1. Technical Field
The present invention relates to a joint structure in which a copper wire and an aluminum wire are electrically connected to each other by means of a joint terminal, and a joint method for obtaining the joint structure.
2. Background Art
The joint terminal has been used for direct connection between electric wires (For example, see JP-A-9-180848). The joint terminal is a terminal having a U-shape in cross section, which includes a bottom plate, and a pair of conductor caulking pieces provided upright at both side edges of the bottom plate and adapted to be folded inwardly so as to enclose conductors of the electric wires to be connected thereby to caulk the conductors in tight contact with an upper face of the bottom plate.
In case of connecting two covered wires by means of this joint terminal, two conductors (each of the conductors includes a bundle of a plurality of raw wires in a form of twisted wires) which are exposed by stripping coverings are superposed on the bottom plate of the joint terminal, and in this state, a pair of the conductor caulking pieces are folded inwardly and caulked by means of a caulking tool having an upper mold and a lower mold (in other words, a press-fitting tool) so as to enclose the two conductors, whereby the two electric wires are connected.
In a wire harness to be arranged inside a vehicle such as an automobile, copper wires have been generally used. Since it has been difficult to use aluminum wires which are inferior in property such as electrical conductivity, strength, etc. (physical properties), the aluminum wires have been scarcely used. However, in recent years, use of the aluminum wires has been more and more required in consideration of weight reduction of the vehicle, a resulting low fuel cost, and recycling performance.
In case of using the aluminum wire, it is necessary to joint the copper wire and the aluminum wire. For example, it is a main stream that the known electric component such as a connector is produced on the premise that the copper wire is used, and therefore, when the aluminum wire is used, there is such anxiety the same component cannot be used because of differences in size, and so on. Under the circumstances, when the known electric component is used as it is, it is considered that the copper wire is used in a part directly connected to the electric component, while the aluminum wire is used in other parts. In this case, it is necessary to elaborate a structure for jointing the aluminum wire and the copper wire on halfway.
However, joint of the copper wire and the aluminum wire by means of a joint terminal has not been heretofore conducted, and for realizing such joint, both the problem of strength and the problem of electric performance must be cleared. In case where the copper wire and the aluminum wire are actually connected by means of the joint terminal, differences in physical properties such as strength, electrical conductivity must be taken into consideration. At the same time, presence of oxidation layer on the conductor formed of aluminum or aluminum alloy must be fully considered, but not sufficiently considered at present.